Many regulations exist for the treatment and discharge of ballast water by marine vessels. Ship ballast water treatment systems are typically tested by an independent laboratory. These laboratories, even when following mandated test protocols, are not able to replicate all of the variability in organism populations, water chemistry, and environmental conditions that a marine vessel will encounter during operations. This leads to uncertainty that ballast water treatment systems will be effective in varied conditions. Marine vessel operators and regulatory agencies need tools and methods for reliable sampling of ballast water to allow these determinations to be made.